BGA Solder Joint Composition for Thermal Fatigue Resistance
Solution Overview
Problem
Existing BGA mounting structures fail to provide sufficient thermal fatigue resistance at high temperatures, such as those encountered in an automobile engine room, leading to potential disconnection and loss of electric conduction due to the generation of hard proeutectic Cu6Sn5 intermetallic compounds and inadequate ductility in the solder joining portion.
Innovation Solution
A BGA mounting structure with a solder joining portion composed of a specific alloy ratio of Cu, Ag, Bi, In, and Sn, where the Cu content is between 0.6% and 1.2% mass, and In content is within specific ranges based on the Cu ratio, preventing the formation of proeutectic Cu6Sn5 and promoting the formation of (Cuy,Ni1-y)6Sn5, enhancing thermal fatigue resistance and maintaining electric conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BGA ball with high Cu content (≥3 mass%) is used to improve electric conduction, then electric conduction is enhanced, but thermal fatigue resistance deteriorates due to formation of hard proeutectic Cu6Sn5 intermetallic compounds
Solution Approach 1:
The patent changes the compositional parameters of the BGA ball by precisely controlling Cu content to 0.6-1.2 mass% and In content to 5.3-6.8 mass%, along with Ag (3.0-4.0 mass%) and Bi (0.1-1.0 mass%). This parameter optimization prevents excessive Cu6Sn5 formation while ensuring adequate electric conduction, resolving the contradiction between conduction and thermal fatigue resistance
Solution Approach 2:
The patent applies local quality control by optimizing the distribution and concentration of specific elements within the solder joining portion. The controlled Cu content (0.6-1.2 mass%) ensures adequate conduction at the interface, while the controlled In content (5.3-6.8 mass%) and Bi content (0.1-1.0 mass%) locally enhance ductility and suppress harmful intermetallic formation in the solder matrix, achieving both conduction and thermal fatigue resistance in different regions of the solder joint
2Ease of manufacture
If conventional solder composition is used to simplify manufacturing, then ease of manufacture is improved, but thermal fatigue resistance deteriorates in high temperature environments
Solution Approach 1:
The patent establishes specific compositional parameters (Cu: 0.6-1.2 mass%, In: 5.3-6.8 mass%, Ag: 3.0-4.0 mass%, Bi: 0.1-1.0 mass%) that can be directly applied in manufacturing. These parameter specifications provide clear manufacturing guidelines while achieving the dual goals of thermal fatigue resistance and electric conduction, making the complex composition manageable through defined ranges
Solution Approach 2:
The solder alloy composition is designed to self-regulate the formation of intermetallic compounds during the soldering process. The controlled Cu and In content, along with Bi addition, enables the solder to automatically suppress excessive Cu6Sn5 formation and promote ductile phase formation under standard soldering conditions, reducing the need for additional manufacturing process controls
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution significantly improves thermal fatigue resistance, ensuring electric conduction beyond 3000 cycles in temperature cycle tests, meeting on-board standards by preventing crack growth and disconnection in high-temperature environments.
Implementation Method 1
solder paste layer 110 is heated to the melting point thereof through an arbitrary method using hot air, an infrared ray, or the like, and thus solder paste layer 110 and BGA ball 101 are melted
Implementation Method 2
heated to the melting point thereof through an arbitrary method using hot air, an infrared ray, or the like
Implementation Method 3
preventing the formation of proeutectic Cu6Sn5 and promoting the formation of (Cuy,Ni1-y)6Sn5
Data Source
AI summary
A mounting structure includes a BGA including a BGA electrode, a circuit board including a circuit board electrode, and a solder joining portion which is arranged on the circuit board electrode and is connected to the BGA electrode. The solder joining portion is formed of Cu having a content ratio in a range from 0.6 mass % to 1.2 mass %, inclusive, Ag having a content ratio in a range from 3.0 mass % to 4.0 mass %, inclusive, Bi having a content ratio in a range from 0 mass % to 1.0 mass %, inclusive, In, and Sn. A range of the content ratio of In is different according to the content ratio of Cu.